This invention relates to the type of gas filtering apparatus known in the gas cleansing art as a baghouse filter. Such baghouse filters commonly include an enclosure or housing which encloses an array of elongated, tubular filter bags and a hopper or dust collection bin subjacent to the filter bags and separated therefrom by a partition known as a thimble floor or tube sheet. The tube sheet includes a plurality of flanged perforations, each of which flanges is adapted to have secured thereto the open end of the filter bag whereby the interior of the filter bag communicates through the respective perforation with the dust collection bin. The baghouse is provided with suitable ductwork and valve or damper means whereby dirty effluent gas to be filtered may be passed through the perforations in the tube sheet into the interior of each respective filter bag and thence through the fabric of the filter bags whereby dust or other foreign particulate matter entrained in the gas stream is arrested in the well known manner. The cleansed effluent gas is then passed from the baghouse enclosure to the atmosphere by way of suitable outlet or exhaust means. Periodically, the filter bags are cleaned as by rapping or by reverse flow of air or gas through the bag fabric to collapse the bags and dislodge the collected duct adhering to the interior of the bag. The dust then falls lengthwise of the bags and through the respective tube sheet perforations into the dust collection bin for subsequent disposal.
Although many such prior baghouse filters have generally served their intended purposes they have nevertheless been subject to certain limitations. For example, a pitched roof has been provided for many prior baghouse enclosures to limit snow loading, eliminate rain water accumulation problems and the like. One such roof structure is illustrated in U.S. Pat. No. 3,266,225. Although providing certain benefits as noted, pitched roof designs known heretofore have resulted in substantial wasted interior space directly beneath the roof within the enclosure inasmuch as the uniform length filter bags commonly used have extended upwardly a fixed distance from the flat thimble floor and have therefore terminated at a common level below the lowest interior extent of the pitched roof. In the prior art the only way to avoid such wasted space has been to use non-uniform filter bags of different length.
In a more general context it will be seen that the design parameters of prior baghouse enclosures often have been dictated in part by factors unrelated to the desired filtering capacity of the unit. This in turn has led to the construction of enclosures which are larger than absolutely necessary for the desired filtering capacity and this is particularly undesirable in the technology of unitized or modular baghouse structures which are fabricated in the plant for shipment as a completed unit to an assembly site as opposed to being fabricated on site.
Another aspect of baghouse design that has received considerable attention is personnel safety. For example, normal baghouse filter operating procedures call for periodic inspection and replacement of the filter bags which are subject to progressive wear during the successive filtering and cleaning cycles. Thus, in prior baghouses various configurations of both thimble floor passages and elevated walkways have been provided whereby personnel may gain the required access to all of the filter bags. Various approaches to ensure the safety of these personnel during baghouse inspections have been proposed. For example U.S. Pat. No. 3,850,596 discloses a baghouse including elevated walkways which are wider than conventional baghouse walkways, and which, in fact, are wider than the spacing between the groupings or banks of filter bags on either side thereof. To obviate problems of physical interference with the adjacent filter bags, the walkways are provided with pivot means whereby they may be selectively pivoted to a noninterfering position when not in use.
Filter bag cleaning apparatus and processes are another area which has received considerable attention in the art inasmuch as effective filter bag cleaning is necessary for efficient filter operation. Prior approaches to filter bag cleaning have included rapping devices of various designs, and the use of gas pressure differentials imposed across the fabric of the filter bags for cleaning thereof. For example, with regard to this latter approach U.S. Pat. No. 3,266,225 discloses filter bag cleaning by gradual deflation of the filter bags through the gradual imposition of a reverse gas flow inwardly through the bag fabric and into the interior of the filter bags. Subsequently, the reverse gas flow is terminated and the normal gas flow quickly re-established to rapidly reinflate the filter bags thereby physically shaking the bags to dislodge the dust therefrom.
The present invention contemplates novel improvements to these and other aspects of baghouse filters including but not limited to elimination of wasted space directly beneath the pitched roof of a baghouse enclosure, and improved elevated walkway arrangements whereby the walkway is widened in conjunction with an overall narrowing of the housing structure and without any substantial reduction in the baghouse filtering capacity or any adverse effect on operational characteristics. An additional improvement according to the present invention involves a novel process and apparatus for reverse gas flow to provide superior filter bag cleansing.